Orthotropic Steel Deck (OSD) systems have been widely utilized in bridge construction globally, owing to their numerous advantages, notably their high load-bearing capacity and relatively low dead weight. However, OSD bridges, particularly those constructed before the introduction of fatigue design codes in 1994, are susceptible to fatigue damage, primarily due to the presence of numerous welded joints. This study presents a comprehensive analytical investigation into the application of an Orthotropic-composite slab for rehabilitating existing OSD bridges. The composite action in the modified deck is primarily achieved through the incorporation of dowel strips in a clothoid (CL) shape, with ongoing testing and evaluation for potential inclusion in design codes. An evaluation of performance is also conducted by comparing the composite slab utilizing dowel strips with the conventional composite slab employing shear-headed studs. Aligned with Eurocode criteria introducing diverse fatigue detail categories for OSD bridges, the efficacy of the proposed modification approach is appraised. This assessment focuses on enhancing structural performance and fatigue resistance, employing finite element analysis conducted through ABAQUS software. A numerical parametric study determines the impact of variables such as the arrangement of dowel strips and the application of transverse or longitudinal rows of dowel strips. The findings demonstrate that when implemented in specific configurations, the modification method can significantly reduce stress ranges at critical hot spots, effectively bringing them below the designated cut-off limit. This research represents progress toward enhancing the durability and economic feasibility of OSD bridge rehabilitation, with promising implications for bridge engineering.